Particular embodiments fall within the field of telecommunication, particularly within the field of DSSS telecommunication systems (direct sequence spread spectrum), in which transmit-side with the use of first sequences, such as, e.g., PN sequences (pseudo noise), band spreading occurs, which is canceled receiver-side by a corresponding despreading with use of second sequences, whereby every second sequence is assigned to a first sequence and can be derived therefrom or is even identical thereto.
The number of levels of the second sequences employed receiver-side, i.e., the number of different values that the chips of the second sequences assume, corresponds in known DSSS telecommunication systems to the number of levels of the first sequences used transmit-side. If the chips of the first sequences assume, e.g., the two logic values zero and one or—equivalent hereto—the two antipodal values ±1, then typically also in the receiver two-level second sequences are used, whose chips assume precisely two different values, e.g., zero and one or ±1.
It is a disadvantage here that with expected interference effects, such as distortions, e.g., by typical transmission channels and/or degradations due to the specific receiver realization, the error probability (symbol, bit, frame error rate, etc.) in the data symbol decision is relatively high without further countermeasures and thereby the efficiency of the detection is relatively low. Countermeasures to increase efficiency, such as, e.g., advanced equalization or MLSE techniques (maximum likelihood sequence estimation) or improved receiver realizations typically involve higher implementation costs and/or increased power consumption by the transmitting/receiving device.
Overview
Particular embodiments provide a detection unit and a method for the detection of data symbols contained in a demodulated signal, which also achieve a low error probability under expected interference effects and, moreover, enable transmitting/receiving devices that are simple to implement and save power during operation. Furthermore particular embodiments provide a transmitting/receiving device and an integrated circuit.
The detection unit in particular embodiments for the detection of data symbols contained in a demodulated signal, whereby band spreading occurs transmit-side with the use of first sequences, whose first chips each assume one of two different first values, comprises: a) a sequence providing unit, which is designed to provide a group of second sequences with at least one second chip, whereby each second sequence is assigned to a first sequence and each second chip assumes one specific value of at least two different second values, which differ amount-wise from the first values, and whereby the group has at least one second sequence that has a higher level than the first sequences, b) a correlation unit that is connected to the sequence providing unit and is designed to calculate correlation results by correlating the demodulated signal with each second sequence of the group, and c) an evaluation unit that is connected to the correlation unit and is designed to derive the values of the data symbols by evaluating the correlation results.
In particular embodiments, the transmitting/receiving device and the integrated circuit can each have this type of detection unit.
In particular embodiments, a method for the detection of data symbols contained in a demodulated signal, whereby band spreading occurs transmit-side with the use of first sequences, whose first chips each assume one of two different first values, comprises the following steps: a) provision of a group of second sequences with at least one second chip, whereby each second sequence is assigned to a first sequence and each second chip assumes one specific value of at least two different second values, which differ amount-wise from the first values, and whereby the group has at least one second sequence that has a higher level than the first sequences, b) calculation of the correlation results by correlating the demodulated signal with each second sequence of the group, and c) deriving the values of the data symbols by evaluating the correlation results.
Particular embodiments despread the demodulated signal with use of a group of second sequences, which has at least one second sequence that is a higher level than the first sequences used transmit-side and therefore in comparison with the first sequences can assume a higher number of different values. In the two-level first sequences, whose chips (“first chips”), for example, each assume one of the two values ±1 or 0.1 (“first values”), at least one second sequence of the group has at least one chip (“second chip”) that assumes one of at least two “second” values (e.g., ±2 or ±2, ±4) that differ amount-wise from the first values.
This may make it possible to correctly detect (decide) the demodulated signal also under expected interference effects, such as distortions, e.g., by typical transmission channels and/or degradations due to the specific receiver realization, so that the error probability (symbol, bit, frame error rate, etc.) of the detection decreases, when the data symbols are transmitted, e.g., over typical distorting transmission channels such as frequency-selective multipath channels or time-variant and frequency-selective mobile radio channels and/or the received signal experiences additional distortions, e.g., by a receiving filter, is quantified with a bit width of only a few bits, etc.
Particular embodiments are very simple to realize, so that implementations of the detection unit and thereby the transmitting/receiving device, which are simple in design and power-saving to operate, become possible. This is advantageous particularly when—as in applications in industrial monitoring and control, sensor networks, and automation, or in the field of computer peripherals—an extremely low power requirement and a very simple realization are indispensable. Although particular embodiments are not limited to the IEEE standard 802.15.4, this is the case by way of example in transmitting/receiving devices for this communication standard.
In particular embodiments of the detection unit or the method, the value of the at least one second chip or/and its chip position within its second sequence are selected in such a way that the error probability of detection due to the correlation decreases with this second sequence, when the data symbols are transmitted over at least one typical transmission channel.
The efficiency of the detection improves as a result of selecting the values of the second chips of a second sequence and/or the chip positions of the second chips within this second sequence in such a way that the error probability of the detection in a transmission of the data symbols over at least one typical (specified) transmission channel decreases.
In particular embodiments, the number of second chips, present in a second sequence, is selected in such a way that a number of second chips, exceeding this number, does not cause a major decrease in the error probability of detection, when the data symbols are transmitted over at least one typical transmission channel. This enables especially simple implementations.
In particular embodiments, each second chip assumes one specific value of at least two different second values, which each correspond amount-wise to an integer positive power of two. This enables especially simple implementations at a low error probability, because the receiver-side correlation unit need not perform real multiplications.
Each second chip can assume one specific value of four different second values, which correspond amount-wise to the 2× or 4× value of one of the first values. This facilitates especially simple implementations.
Each second chip can assume one specific value of two different second values, which correspond amount-wise to the 2× value of one of the first values. This enables especially simple implementations.
In particular embodiments, the sign of each second chip of a second sequence agrees with the sign of the positionally equivalent chip of the two-level sequence, usable receiver-side, that is assigned to the first sequence to which this second sequence is assigned. Because the signs of the second chips each agree with the sign of the particularly positionally equivalent (i.e., index-equivalent) chip of the two-level sequence, actually usable receiver-side, the error probability and the implementation cost are reduced.
In particular embodiments, each second sequence can have at least one third chip, which in each case assumes one of two different third values, which agree amount-wise with one of the first values. This enables especially simple implementations. In addition, this also avoids the case, disadvantageous for the efficiency, that all chip values of a second sequence differ only in a fixed factor (i.e., the same from chip index to chip index) from the index-wise corresponding chip values of a two-level sequence actually to be used receiver-side.
In every second sequence the total number of the second and third chips can agree with the number of the chips present overall in this second sequence. Thereby, no chips, which have neither one of the first nor one of the second values, are present in the second sequences, which simplifies implementation.
In particular embodiments of the detection unit, the group provided by the sequence providing unit comprises a total of n≧1 second sequences, whereas the correlation unit has n multiplication units and n downstream integration units, whereby the multiplication units, each connected to the sequence providing unit, calculate n product signals by multiplying (individually delayed or not delayed) signal values of the demodulated signal by chip values in each case of one of the second sequences, and then each integration unit provides a correlation result by adding a number of signal values of the corresponding product signal. This type of realization of the correlation unit is very simple, requires very little operating energy, and enables a high efficiency in the detection error rate.
The multiplication units can have a device for sign reversal and a device for bit shifting. The hardware expenditure and power consumption of the detection unit are reduced further thereby.
In particular embodiments, the sequence providing unit has precisely one memory, which is designed to store precisely one (i.e., and only one) of the second sequences. A memory, whose size is dimensioned in this way, can be advantageously very simply implemented and operated by saving power.
The memory can be made as a feedback shift register. The very simple structure of a shift register of series-connected register cells makes possible a very efficient and simple realization of the sequence providing unit with a very low power requirement. Thus, e.g., neither calculation of memory addresses nor a complex control logic is required for the shift register.
The sequence providing unit provides the second sequences at the outputs of the specific (several) register cells of the shift register. For this purpose, means are provided for clocking the feedback shift register. All second sequences of the group with or without a time offset among each other can be provided very simply in this way.